1. Field
The present invention relates to devices, systems, and processes useful as a control system for a vehicle drivetrain, and in particular, for automatically selecting components and/or characteristics for a vehicle drivetrain.
2. Description of the Related Art
Typical vehicle drivetrains can be configured as either two-wheel-drive (e.g., front-wheel drive or rear-wheel drive) or all-wheel drive (e.g., part-time or full-time). One example of a part-time, all-wheel-drive vehicle drivetrain is described in U.S. Pat. No. 5,135,071 to Shibahata et al. In a part-time, all-wheel-drive configuration, the vehicle drivetrain operates primarily in a two-wheel-drive configuration and the vehicle is propelled by primary drive wheels (e.g., front wheels) and the secondary drive wheels (e.g., rear wheels) are selectively engaged to improve tractive effort as conditions warrant. The secondary drive wheels are disengaged to maximize fuel efficiency in conditions where two-wheel-drive propulsion is sufficient. Engagement/disengagement of the secondary drive wheels can be initiated by the vehicle operator through a mechanical linkage or via an electrical switch and electro-mechanical actuator assembly. Alternatively, a passive hydro-mechanical system can be utilized, such as that disclosed by Shibahata et al. Another alternate approach to engage/disengage the secondary drive wheels can employ an electronic control unit (ECU) to engage/disengage the secondary drive wheels via an actuator assembly in electrical communication with the ECU.
Certain all-wheel drive vehicles, such as sports-utility vehicles (SUVs) and pick-ups, are used for towing and hauling heavy loads. To further supplement tractive effort when towing or hauling heavy loads, the drivetrain of these types of vehicles can include a range gearbox in series with the multi-ratio transmission. The range gearbox typically includes a gear reduction assembly that provides a high range drive ratio for normal driving speeds and a low range drive ratio for low driving speeds such as when the vehicle is driven off-road, when high torque is desired, when low traction surfaces exist, etc. For example, the low range drive ratio can be used when starting from a stop on an incline with a heavy load or with a trailer in tow (i.e., when engine load is high). Each of the high range drive ratio and the low range drive ratio can be used with any one of the reverse drive ratio and the plurality of forward drive ratios available in the multi-ratio transmission. The vehicle operator can select and engage/disengage the low range drive ratio or the high range drive ratio via a mechanical linkage or via an electrical switch and electro-mechanical actuator assembly.
U.S. Patent Application No. 2005/0004732 to Berry et al. and U.S. Pat. No. 7,349,776 to Spillane et al. each disclose an exemplary vehicle drivetrain that includes selection and engagement/disengagement of the high or low range drive ratios via a switch positioned by the vehicle operator. Further, positioning of the switch by the operator of the vehicle can toggle the rear differential between a locked position and an unlocked position. Because these drivetrains rely on actuation of a switch by the operator, selection and engagement/disengagement of the low or high range drive ratio and/or locking/unlocking of the rear differential is not fully automated.
Accordingly, there is a need for a fully automated control of the selection, engagement and/or modulation of various components of the vehicle drivetrain without a specific and deliberate prompt from the vehicle operator, as well as to provide operating parameters for an ECU that provide efficient and accurate automatic selection/modulation of the drivetrain components.